1. Field of the Invention
The present invention relates to a magnetoresistive head for use in a magnetic recording device such as a magnetic disk drive and a magnetic tape drive, and more particularly to a spin valve magnetoresistive head.
2. Description of the Related Art
In association with a reduction in size and an increase in recording density of a magnetic disk drive in recent years, the flying height of a head slider has become smaller and it has been desired to realize contact recording/reproduction such that the head slider flies a very small height above a recording medium or comes into contact with the recording medium.
Further, a conventional magnetic induction head has a disadvantage such that its reproduction output decreases with a decrease in peripheral speed of a magnetic disk as the recording medium (relative speed between the head and the medium) caused by a reduction in diameter of the magnetic disk. To cope with this disadvantage, there has recently extensively been developed a magnetoresistive head (MR head) whose reproduction output does not depend on the peripheral speed and capable of obtaining a large output even at a low peripheral speed. Such a magnetoresistive head is now a dominating magnetic head. Further, a magnetic head utilizing a giant magnetoresistive (GMR) effect is also commercially available at present.
With higher-density recording in a magnetic disk drive, a recording area of one bit decreases and a magnetic field generated from the medium accordingly becomes smaller. The recording density of a magnetic disk drive currently on the market is about 20 Gbit/in2, and it is rising at an annual rate of about 200%. It is therefore desired to develop a magnetoresistive head having a narrow core width and a large reproduction output which can support a minute magnetic field range and can sense a change in small external magnetic field.
At present, a spin valve magnetoresistive sensor utilizing a spin valve GMR effect is widely used in a magnetic head for a magnetic disk. In such a magnetoresistive sensor having a spin valve structure, a magnetization direction in a free ferromagnetic layer (free layer) is changed by a signal magnetic field from a recording medium, so that a relative angle of this magnetization direction to a magnetization direction in a pinned ferromagnetic layer (pinned layer) is changed, causing a change in resistance of the magnetoresistive sensor.
In the case of using this magnetoresistive sensor in a magnetic head, the magnetization direction in the pinned layer is fixed to a direction along the height of a magnetoresistive element, and the magnetization direction in the free layer in the condition where no external magnetic field is applied is generally designed to a direction along the width of the magnetoresistive element, which direction is perpendicular to the pinned layer. Accordingly, the resistance of the magnetoresistive sensor can be linearly increased or decreased according to whether the direction of the signal magnetic field from the magnetic recording medium is parallel or antiparallel to the magnetization direction of the pinned layer. Such a linear resistance change facilitates signal processing in the magnetic disk drive.
In a magnetoresistive sensor now in use, a sense current is passed in a direction parallel to the film surface of the magnetoresistive element to read a resistance change according to an external magnetic field. In such a case of a CIP (Current In the Plane) structure that a current is passed in a direction parallel to the GMR film surface, the output from the sensor decreases with a decrease in sense region (core width) defined by a pair of electrode terminals. Known as a magnetoresistive head capable of obtaining a large reproduction output with a narrow core width is a so-called terminal overlay type magnetoresistive head having such a structure that the spacing between a pair of terminal layers provided on the opposite sides of a GMR film is set smaller than the spacing between a pair of hard magnetic film bias layers provided beneath the terminal layers.
Further, it is known that a so-called specular type spin valve magnetoresistive head having an oxide film formed on a free layer to generate specular scattering is effective as a GMR element configuration for obtaining a large reproduction output. Further, it is also known that a so-called bottom type or reverse layered type magnetoresistive head having such a structure that a free layer is positioned farther than a pinned layer with respect to a slider substrate in layering a GMR element is advantageous from the viewpoint of efficiently utilizing a bias magnetic field of a bias layer to control a magnetic domain in the free layer.
However, in the case of forming a GMR element by combining all of the above-mentioned configurations, the following problems may arise. In a terminal overlay bottom type specular GMR, an oxide film is formed on a free layer, and a pair of terminal layers are formed on the oxide film in an overlay structure. Accordingly, a sense current supplied from a terminal to the GMR element does not efficiently flow to the GMR element or does not flow at all. Therefore, it is basically impossible to use this GMR element as a magnetoresistive head.
In a terminal overlay top type specular GMR, a free layer having an oxide film on the surface is positioned nearer than a pinned layer with respect to a slider substrate. In this GMR, a bias magnetic field cannot be efficiently applied to the free layer, so that Barkhausen jump is likely to occur. Accordingly, this GMR is not suitable for a magnetoresistive head. Further, in a conventional bottom type specular GMR having no terminal overlay structure, it is difficult to obtain a large reproduction output with a narrow core width.
It is therefore an object of the present invention to provide a magnetoresistive head which can obtain a large reproduction output with a narrow core width.
It is another object of the present invention to provide a manufacturing method for such a magnetoresistive head.
In accordance with an aspect of the present invention, there is provided a magnetoresistive head comprising a first magnetic shield; an antiferromagnetic layer provided on the first magnetic shield; a pinned ferromagnetic layer provided on the antiferromagnetic layer; a nonmagnetic intermediate layer provided on the pinned ferromagnetic layer; a free ferromagnetic layer provided on the nonmagnetic intermediate layer; a pair of hard magnetic film bias layers provided in spaced relationship with each other on the opposite sides of the free ferromagnetic layer; a pair of terminal layers provided on the pair of hard magnetic film bias layers, respectively; a metal oxide film formed on at least the free ferromagnetic layer at an exposed portion between the pair of terminal layers; and a second magnetic shield provided on the pair of terminal layers and the metal oxide film.
Each of the pair of hard magnetic film bias layers is in contact with one end of each of the antiferromagnetic layer, the pinned ferromagnetic layer, the nonmagnetic intermediate layer, and the free ferromagnetic layer. Preferably, the spacing between the pair of terminal layers is smaller than the spacing between the pair of hard magnetic film bias layers, and one end portion of each of the terminal layers is in electrical contact with the free ferromagnetic layer.
The metal oxide film is formed by oxidizing a metal layer preliminarily formed on the free ferromagnetic layer, after forming the pair of hard magnetic film bias layers and the pair of terminal layers. Alternatively, the metal oxide film may be formed by depositing a metal oxide film on the free ferromagnetic layer and the pair of terminal layers after forming the pair of hard magnetic film bias layers and the pair of terminal layers.
In accordance with another aspect of the present invention, there is provided a manufacturing method for a magnetoresistive head, comprising the steps of forming a first magnetic shield; forming an antiferromagnetic layer on the first magnetic shield; forming a pinned ferromagnetic layer on the antiferromagnetic layer; forming a nonmagnetic intermediate layer on the pinned ferromagnetic layer; forming a free ferromagnetic layer on the nonmagnetic intermediate layer; forming a metal layer on the free ferromagnetic layer; forming a pair of hard magnetic film bias layers in spaced relationship with each other on the opposite sides of the free ferromagnetic layer; forming a pair of terminal layers on the pair of hard magnetic film bias layers, respectively; oxidizing the metal layer to form a metal oxide layer; and forming a second magnetic shield on the pair of terminal layers and the metal oxide layer.
Alternatively, a metal oxide film may be formed on the free ferromagnetic layer and the terminal layers after forming the hard magnetic film bias layers and the terminal layers, without preliminary formation of the metal layer on the free ferromagnetic layer.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.